Pulse width modulator with reduced pulse width

ABSTRACT

An integrated circuit includes a pulse width modulator. The pulse width modulator includes a multiplexer that receives a plurality of data delay signals. Each of the data delay signals is based on a data signal and a respective clock phase signal. The multiplexer includes a first multiplexer stage and a second multiplexer stage. The first multiplexer stage receives all of the data delay signals and has a relatively large delay. The second multiplexer stage receives to output signals from the first multiplexer stage and has a relatively small delay. The second multiplexer stage outputs a pulse width modulation signal that can have a pulse width corresponding to the offset between two adjacent clock phase signals.

BACKGROUND Technical Field

The present disclosure is related to integrated circuits, and moreparticularly to integrated circuits with pulse width modulators.

Description of the Related Art

Pulse width modulators are used to generate pulses of variable width. Todo this, the rising edge of a data pulse is delayed by a differentamount than the delay on the falling edge. To achieve this, a phaselocked loop can be used to create phase signals from a clock signalwhich can be used to delay the data edges precisely. By controlling thedelay on the positive and the negative edge, pulse width modulation canbe achieved.

In some cases, it is desirable to have very small pulse width at theoutput of the pulse width modulator. The width of the pulse may need tobe the size of a single unit step, where the unit step is the period ofthe clock signal divided by the number of phase signals generated fromthe clock signal. This can be difficult to achieve.

BRIEF SUMMARY

A pulse width modulator in accordance with principles of the presentdisclosure is able to provide pulses with very small widths. The pulsewidth modulator includes a multiplexer that includes multiple stages.The multiplexer is designed so that the final output stage has a verysmall delay compared with the preceding stages. The preceding stagescollectively have a large delay but are balanced so their output signalsarrive at the final stage with a same delay. The pulse width modulatorcan output pulses with widths as small as the very small delay of thefinal multiplexer stage.

The pulse width modulator generates N phase signals from a clock signal.Each phase signal has the same period T as the clock signal but isdelayed from the clock signal by a respective number of unit stepsranging from 0 unit steps to N−1 unit steps, where a unit step has avalue equal to T/N. When a data signal is received by the pulse widthmodulator, the pulse width modulator generates N data delay signals eachcorresponding to one of the phase signals. Each data delay signalmatches the data signal but is delayed by the number of unit stepscorresponding to the associated phase signal. In one embodiment, eachdata delay signal is delayed by the number of unit steps plus one clockcycle.

Half of the data delay signals are received by a first substage of themultiplexer. The other half of the data delay signals are received by asecond substage of the multiplexer. The first and second substagescorrespond to the first stage of the multiplexer. Each substage providesone of the data delay signals to the final stage. The first and secondsubstages have identical delays. The final substage outputs a pulsehaving a width based on the rising and falling edges of the outputs ofthe first stage. The final stage has a delay that is smaller than asingle unit step. This enables the multiplexer to output a pulse with awidth equal to a single unit step.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Reference will now be made by way of example only to the accompanyingdrawings. In the drawings, identical reference numbers identify similarelements or acts. In some drawings, however, different reference numbersmay be used to indicate the same or similar elements. The sizes andrelative positions of elements in the drawings are not necessarily drawnto scale. For example, the shapes of various elements and angles are notnecessarily drawn to scale, and some of these elements may be enlargedand positioned to improve drawing legibility.

FIG. 1A is a block diagram of a pulse width modulator, according to oneembodiment.

FIG. 1B is a schematic diagram of a multiplexer of the pulse widthmodulator of FIG. 1A, according to one embodiment.

FIG. 2A is a schematic diagram of a pulse width modulator, according toone embodiment.

FIG. 2B is a schematic diagram of a multiplexer of the pulse widthmodulator of FIG. 2A, according to one embodiment.

FIG. 2C is a schematic diagram of selection logic of the pulse widthmodulator of FIG. 2A, according to one embodiment.

FIG. 2D is a timing diagram of signals associated with the pulse widthmodulator of FIG. 2A, according to one embodiment.

FIG. 3 is a flow diagram of a method for generating data pulses,according to one embodiment.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various disclosedembodiments. However, one skilled in the relevant art will recognizethat embodiments may be practiced without one or more of these specificdetails, or with other methods, components, materials, etc.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is, as “including, but not limited to.” Further,the terms “first,” “second,” and similar indicators of sequence are tobe construed as interchangeable unless the context clearly dictatesotherwise.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its broadest sense, that is, as meaning“and/or” unless the content clearly dictates otherwise.

FIG. 1A is a block diagram of a pulse width modulator 100, according toone embodiment. The pulse width modulator 100 is configured to receivean input data signal (DATA IN) and to generate an output data signal(DATA OUT). The output data signal is a pulse having a width thatrepresents the value of the input data signal. As is set forth in moredetail below, the pulse width modulator 100 is able to generate a dataoutput pulse having a very small pulse width.

The pulse width modulator 100 includes a phase locked loop 102. Thephase locked loop 102 receives a clock signal CLK. The clock signal CLKhas a frequency f and period T. The clock signal CLK can include asquare wave form having rising and falling edges.

The pulse width modulator 100 receives the clock signal CLK andgenerates N phase signals P₀-P_(N-1), where N is an integer. Each of thephase signals has the same form, frequency, and period of the clocksignal CLK. Accordingly, the phase signals can be considered clocksignals in form and function. Each of the phase signals is delayed fromthe clock signal by an integer number of unit steps. A single unit stephas a value of T/N. The phase signal P₀ is delayed by 0 unit steps andthus has no delay from the clock signal CLK. The phase signal P₁ isdelayed from the clock signal by a single unit step. The phase signal P₂is delayed from the clock signal by two unit steps. The final phasesignal, P_(N-1) is delayed from the clock signal by N−1 unit steps. Asan illustrative example, the phase signal P₁ is delayed by a single unitstep. This means that the rising edge of the phase signal P₁ is delayedfrom the rising edge of the clock signal CLK by a single unit step, orby a length of time equal to T/N.

The pulse width modulator 100 includes a data delay generator 104. Thedata delay generator 104 is coupled to the phase locked loop 102. Thedata delay generator 104 receives each of the phase signals P₀-P_(N-1)from the phase locked loop 102. The data delay generator 104 alsoreceives a data input signal. The data input signal indicates that datahas been received and that the pulse width modulator 100 should generatean output pulse corresponding to the value of the data signal that hasbeen received and the value of the phase select signal PS_(<k:0>), aswill be described in more detail below. In one embodiment, DATA IN maysimply be an indicator that data has been received. The pulse widthmodulator may receive the actual data value separately.

The data delay generator 104 generates N data delay signals D₀-D_(N-1).Each data delay signal D₀-D_(N-1) is associated with a respective phasesignal. The data delay signal D₀ is associated with the phase signal P₀.The data delay signal P₁ is associated with the phase signal P₁. Thedata delay signal D_(N-1) is associated with the phase signal P_(N-1).

The data delay generator 104 outputs the data delay signals with atiming based on the clock signal CLK, the phase signals, and the datainput signal. In particular, when the data delay generator 104 receivesthe data input signal which is in sync with the rising edge of the clocksignal, the data delay generator begins outputting the data delaysignals upon the next rising edge of the clock signal CLK. Each datadelay signal has a rising edge that is delayed from the rising edge ofthe clock signal by the value of the delay of the phase signal withwhich the data delay signal is associated. For example, when a datainput signal is received, at the next rising edge of the clock signalthe data delay generator will output the data delay signal D₀. Therising edge of the data delay signal D₀ coincides with the rising edgeof the clock signal CLK because the phase signal P₀ with which the datadelay signal D₀ is associated is in sync with the clock signal CLK. Therising edge of the data delay signal D₁ is delayed from the rising edgeof the clock signal by a single unit step because the phase signal P₁associated with the data delay signal D₁ is delayed from the clocksignal by a single unit step. The rising edge of the data delay signalD_(N-1) is delayed from the rising edge of the clock signal by N−1 unitsteps because the associated phase signal P_(N-1) is delayed from theclock signal by N−1 unit steps.

The pulse width modulator 100 includes a multiplexer 106. Themultiplexer 106 is coupled to the data delay generator 104. Inparticular, the multiplexer 106 receives each of the data delay signalsD₀-D_(N-1) from the data delay generator 104. The multiplexer 106outputs a data output pulse having a width corresponding to the value ofthe data associated with the data input signal.

The multiplexer 106 receives a phase select signal PS_(<k:0>), orvarious selection signals generated from the phase select signal byselection logic not shown in FIG. 1A. The phase select signal PS_(<k:0>)is a data signal that selects or controls the width of the output datapulse from the multiplexer 106. The phase select signal has k+1 bits,where k=log₂(N)−1. The phase select signal includes information thatcauses the multiplexer to select input data delay signals to be providedat the output of the multiplexer. In this way, the phase select signalPS_(<k:0>) controls the width of the output data pulse.

In one embodiment, the rising and falling edges of the data input signalare delayed by the amount represented by the decimal equivalent of thephase select signal PS_(<k:0>) at that edge. Therefore, by varying thedelays at the rising and falling edges of the data input, the outputpulse width can be modulated.

Traditional multiplexers may not be able to output a data output pulsehaving a width corresponding to a single unit step. This is because theinternal delay associated with a multiplexer may be larger than a singleunit step. In traditional multiplexers, the result is that the minimumwidth of the output pulse is equal to the total delay of themultiplexer, which is longer than a single unit step.

The pulse width modulator 100 overcomes the drawbacks of traditionalpulse width modulators by providing a multiplexer 106 that has identicaldelays for all data paths and that has a final stage that has a delaythat is less than a single unit step. The multiplexer 106 of the pulsewidth modulator 100 includes high delay stages 108 and a low delay stage110. The high delay stages 108 are in parallel with each other andcollectively receive all of the data delay signals D₀-D_(N-1) from thedata delay generator 104.

In one example, the high delay stages 108 include a first high delaystage and a second high delay stage. The first high delay stage receiveshalf of the data delay signals. The second high delay stage receives theother half of the data delay signals. The first and second high delaystages are in parallel with each other and are identical to each other.This means that the first and second high delay stages of the high delaystages 108 have identical delays. The first high delay stage outputs afirst midpoint signal. The second high delay stage outputs a secondmidpoint signal. The first and second midpoint signals correspond to therespective data delay signal being output by the high delay stages.

The low delay stage 110 receives first midpoint signal and the secondmidpoint signal. In one example, the first midpoint signal controls therising edge of the data output signal and the second midpoint signalcontrols the falling edge of the data output signal. However, either ofthe midpoint signals can control either edge of the data output signal,depending on the particular situation. The low delay stage has a delaythat is smaller than a single unit step. The low delay stage 110 outputsa data pulse that has a delay smaller than a single unit step and isthus able to output the data pulses with a width of a single unit step,if the data value calls for such a small pulse.

FIG. 1B is a schematic diagram of the multiplexer 106 of FIG. 1A,according to one embodiment. The multiplexer 106 includes a first highdelay stage 108 a and a second high delay stage 108 b. The first highdelay stage 108 a receives the data signals D₀-D_(N/2-1). The secondhigh delay stage 108 b receives the data delay signals D_(N/2)-D_(N-1).Accordingly, each of the first and second high delay stages receiveshalf of the data delay signals.

The first high delay stage 108 a receives a selection signalS_(1<k-1:0>). The selection signal S_(1<k-1:0>) determines the datadelay signal that will be output from the high delay multiplexer 108 a.In the example of FIG. 1B, the selection signal S_(1<k-1:0>) is latchedto the phase signal P_(3N/4). This means that the first high delay stage108 a can output a data delay signal after the next rising edge of thephase signal P_(3N/4). The selection signal S_(1<k-1:0>) has k bitsbecause it can select from N/2 possible data delay signals.

The second high delay stage 108 b receives a selection signalS_(2<k-1:0>). The selection signal S_(2<k-1:0>) determines the datadelay signal that will be output from the high delay stage 108 b. In theexample of FIG. 1B, the selection signal S_(2<3:0>) is latched to thephase signal P_(N/4). This means that the second high delay stage 108 bcan output a data delay signal after the next rising edge of the phasesignal P_(N/4).

The low delay stage 110 receives the midpoint signals from the first andsecond high delay stages 108 a, 108 b. The low delay stage 110 outputs adata output pulse having a width that represents a data value associatedwith the data input signal. The low delay stage 110 receives a selectionsignal S_(3′). The selection signal S_(3′) is the generated signal S₃with the added delay of the multiplexer. The selection signal S₃ islatched to the phase signal P_(N-1). The rising and falling edges of thedata can be triggered by either the first or second midpoint signalbased on the polarity of S_(3′).

FIG. 2A is a block diagram of a pulse width modulator 100, according toone embodiment. The pulse width modulator 100 includes a phase lockedloop 102. The phase locked loop 102 receives the clock signal andgenerates 32 phase signals P₀-P₃₁ substantially as described in relationto the phase locked loop 102 of FIG. 1 . In the example of FIG. 2A,N=32. The first phase signal P₀ has no delay relative to the clocksignal CLK. The second phase signal P₁ is delayed from the clock signalCLK by one unit step or 1/32 of the period T of the clock signal. Thephase signal P₃₁ is delayed from the clock signal CLK by 31 unit steps,or 31/32 of the period T of the clock signal CLK.

The pulse width modulator 100 includes a data delay generator 104. Thedata delay generator 104 generates 32 data delay signals D₀-D₃₁. Eachdata delay signal D₀-D₃₁ is associated with a respective phase signal,substantially as described in relation to FIG. 1A. The data delaygenerator 104 also receives a data input signal (DATA IN). The datainput signal indicates that data has been received and that the pulsewidth modulator 100 should generate an output pulse corresponding to thevalue of the data signal that has been received. A phase select signalPS_(<4:0>) determines the amount of delay to be added at the DATA INedge, as will be described in more detail below. Both the data inputsignal and PS_(<4:0>) are synchronous to the rising edge of the clocksignal CLK. While FIG. 2A illustrates the phase select signal PS_(<4:0>)as being received by the multiplexer 102, in practice the phase selectsignal may be received by selection logic 150 that generates selectionsignals S1 _(<3:0>), S_(2<3:0>), and S₃ based on the phase select signalPS_(<4:0>).

The data delay generator 104 outputs the data delay signals with atiming based on the clock signal CLK, the phase signals, and the datainput signal. In particular, when the data delay generator 104 receivesthe data input signal, the data delay generator begins outputting thedata delay signals upon the next rising edge of the clock signal CLK.Each data delay signal has a rising edge that is delayed from the risingedge of the clock signal by the value of the delay of the phase signalwith which the data delay signal is associated. For example, when a datainput signal is received, at the next rising edge of the clock signal,the data delay generator will output the data delay signal D₀. Therising edge of the data delay signal D₀ coincides with the rising edgeof the clock signal CLK because the phase signal P₀ with which the datadelay signal D₀ is associated is in sync with the clock signal CLK. Therising edge of the data delay signal D₁ is delayed from the rising edgeof the clock signal by a single unit step because the phase signal P₁associated with the data delay signal D₁ is delayed from the clocksignal by a single unit step. The rising edge of the data delay signalD₃₁ is delayed from the rising edge of the clock signal by 31 unit stepsbecause the associated phase signal P₃₁ is delayed from the clock signalby 31 unit steps.

The data delay circuit 104 includes a plurality of flip-flops. A firstflip-flop 118 receives the data input signal on a data input terminal.The flip-flop 118 receives the phase signal P₁₆ on a clock inputterminal. The flip-flop 120, the flip-flop 121, the flip-flop 122, andthe flip-flop 123 each receive on their data input terminals, the outputof the flip-flop 118. The flip-flop 120 receives the phase signal P₀ asa clock signal and generates the corresponding data delay signal D₀. Theflip-flop 121 receives the phase signal P₁ as a clock signal andgenerates the corresponding data delay signal D₁. The flip-flop 122receives the phase signal P₂ as a clock signal and outputs thecorresponding data delay signal D₂. The flip-flop 123 receives the phasesignal P3 as a clock signal and outputs the corresponding data delaysignal D3.

The flip-flops 124, 125, 126, and 127 receive on the data inputterminals the outputs of the flip-flops 120, 121, 122, and 123respectively. The flip-flops 124, 125, 126, and 127 receive as clocksignals, phase signals P₄₋₇, respectively, and output corresponding datadelay signals D₄₋₇, respectively. The flip-flops 138, 139, 140, and 141receive as clock signals phase signals P₂₈-P₃₁, respectively, and outputdata delay signals D₂₈-D₃₁, respectively.

The flip-flops associated with data delay signals D₈-D₂₇ are not shownin FIG. 2A, but they are present in the circuit and their function canbe understood in relation to the flip-flop shown in FIG. 2A. Though notshown in FIG. 2A, the flip flops associated with the phase signals P₈,P₁₂, P₁₆, P₂₀, and P₂₄ are connected in series between the flip slops124 and 138 and output corresponding data signals D₈, D₁₂, D₁₆, D₂₀, andD₂₄ to the multiplexer 106. Though not shown in FIG. 2A, the flip flopsassociated with the phase signals P₉, P₁₃, P₁₇, P₂₁, and P₂₅ areconnected in series between the flip-flops 125 and 139 and outputcorresponding data signals D₉, D₁₃, D₁₇, D₂₁, and D₂₅ to the multiplexer106. Though not shown in FIG. 2A, the flip flops associated with thephase signals P₁₀, P₁₄, P₁₈, P₂₂, and P₂₆ are connected in seriesbetween the flip slops 126 and 140 and output corresponding data signalsD₁₀, D₁₄, D₁₈, D₂₂, and D₂₆ to the multiplexer 106. Though not shown inFIG. 2A, the flip flops associated with the phase signals P₁₁, P₁₅, P₁₉,P₂₃, and P₂₇ are connected in series between the flip slops 127 and 141and output corresponding data signals D₁₁, D₁₅, D₁₉, D₂₃, and D₂₇ to themultiplexer 106. In the context above, the flip flops connected “inseries” means that the data output terminal of one flip flop isconnected to the data input terminal of the next flip flop, though theyhave different clock inputs. The multiplexer 106 receives all of thedata delay signals D₀-D₃₁.

FIG. 2B is a schematic diagram of the multiplexer 106 of FIG. 2A,according to one embodiment. The multiplexer 106 includes a first highdelay stage 108 a and a second high delay stage 108 b. The first highdelay stage 108 a receives the data signals D₀-D₁₅. The second highdelay stage 108 b receives the data delay signals D₁₆-D₃₁. Accordingly,each of the first and second high delay stages receives half of the datadelay signals.

The first high delay stage 108 a receives a selection signal S_(1<3:0>).The selection signal S_(1<3:0>) is a four bit input signal S_(1<3:0>).The selection signal S_(1<3:0>) determines the data delay signal thatwill be output from the high delay multiplexer 108 a. In the example ofFIG. 2B, the selection signal S_(1<3:0>) is latched to the phase signalP₂₄ as all of the inputs to the first high delay stage 108 a are on thesame value at this time and hence no glitches will occur when S_(1<3:0>)switches. This means that the first high delay stage 108 a can output adata delay signal after the next rising edge of the phase signal P₂₄. Ingeneral, it is beneficial for the selection signal S_(1<3:0>) to belatched to a phase signal associated with the group of data signalsreceived by the second high delay stage 108 b. In one embodiment, it isparticularly beneficial for the selection signal S_(1<3:0>) to belatched to the phase signal P_(3N/4), or in the case where N=32, P₂₄.

The second high delay stage 108 b receives a selection signalS_(2<3:0>). The selection signal S_(2<3:0>) is a four bit input signalS_(2<3:0>). The selection signal S_(2<3:0>) determines the data delaysignal that will be output from the high delay stage 108 b. In theexample of FIG. 1B, the selection signal S_(2<3:0>) is latched to thephase signal P₈ as all of the inputs to the second high delay stage 108b are on the same value at this time and hence no glitches will occurwhen S_(2<3:0>) switches. This means that the second high delay stage108 b can output a data delay signal after the next rising edge of thephase signal P₈. In general, it is beneficial for the selection signalS_(2<3:0>) to be latched to a phase signal associated with the group ofdata signals received by the first high delay stage 108 a. In oneembodiment, it is particularly beneficial for the selection signalS_(2<3:0>) to be latched to the phase signal P_(N/4), or in the casewhere N=32, P₈.

The first high delay stage 108 a outputs a midpoint signal M_(U). M_(U)corresponds to the data delay signal selected by S_(1<3:0>). The secondhigh delay stage 108 b outputs a midpoint signal M_(L). M_(L)corresponds to the data delay signal selected by S_(2<3:0>).

The low delay stage 110 receives the midpoint signals M_(U), M_(L) fromthe first and second high delay stages 108 a, 108 b. The low delay stage110 outputs a data output pulse having a width that represents a datavalue associated with the data input signal. The low delay stage 110receives a selection signal S_(3′). The selection signal S_(3′) islatched to the phase signal P₃₁. The rising edge of the data outputpulse may be triggered by the edge of either the midpoint signal M_(U)output by the first high delay stage 108 a or the edge of the midpointsignal M_(L). The falling edge of the data output pulse may be triggeredby the edge of either the midpoint signal M_(L) output by the secondhigh delay stage 108 b or the edge of the midpoint signal M_(U) outputby the first high delay stage 108 a.

FIG. 2C is a block diagram of selection logic 150, according to oneembodiment. The selection logic 150 generates the selection signalsS_(1<3:0>), S_(2<3:0>), and S₃. A flip-flop 152 receives a phase selectsignal PS_(<3:0>) on a data input terminal and the phase signal P₂₄ onthe clock input terminal and outputs the selection signal S_(1<3:0>).While a signal flip flop 152 is illustrated in FIG. 2C, in practicethere are four flip flops 152 that each receive a respective bit of thephase select signal PS_(<3:0>) on the data input terminal and the phasesignal P₂₄ the clock input terminal. The selection signal S_(1<3:0>) isa four bit signal with each bit being supplied by one of the four flipflops 152.

A second flip-flop 154 receives the selection signal S_(1<3:0>) on adata input terminal and the phase signal P₈ on the clock input terminaland outputs the selection signal S_(2<3:0>). While a signal flip flop154 is illustrated in FIG. 2C, in practice there are four flip flops 154that each receive a respective bit of the selection signal S_(1<3:0>) onthe data input terminal and the phase signal P₈ the clock inputterminal. The selection signal S_(2<3:0>) is a four bit signal with eachbit being supplied by one of the four flip flops 152.

A third flip-flop 156 receives the phase select signal PS_(<4>) on thedata input terminal and the phase signal P₃₁ on the clock input terminaland outputs the selection signal S₃. Accordingly, the third flip-flopsamples PS_(<4>) at the rising edge of P31 and outputs the selectionsignal S₃. The selection signal S_(3′) is generated from S₃ by adding adelay value to S₃, as will be explained in more detail below.

The phase select signals PS_(<3:0>) and PS_(<4>) indicate the data delaysignals to be utilized in generating the data output pulse. Theselection signals S_(1<3:0>), S_(2<3:0>), and S₃ are provided to themultiplexer 106.

FIG. 2D is an example of a timing diagram of signals associated with thepulse width modulator 100 of FIGS. 2A-2C, according to one embodiment.FIG. 2B illustrates the phase signal P₀, the phase signal P₁₆, and thephase signal P₃₁. The phase signal P₀ is aligned with the clock signalCLK. The phase signal P₁₆ is offset by 16 unit steps from the phasesignal P₀. The rising edge of the phase signal P₁₆ occurs at the fallingedge of the phase signal P₀. The phase signal P₃₁ is 31 unit stepsdelayed from the phase signal P₀. Accordingly, the rising edge of thephase signal P₃₁ occurs 31 unit steps after the rising edge of the phasesignal P₀. FIG. 2D also illustrates the locations of the rising edges ofthe phase signals P₈ and P₂₄ in dashed lines.

FIG. 2D illustrates that a data input signal (DATA IN) is receivedslightly after the rising edge of the phase signal P₀ (also the clocksignal CLK). The phase select signal PS_(<4:0>) has transitions at therising and falling edges of the data input signal. The selection signalS_(1<3:0>) is latched to the phase signal P₂₄ and accordingly hastransitions on the rising edges of P₂₄. The selection signal S_(2<3:0>)is latched to the phase signal P₈ and accordingly has transitions on therising edges of P₈.

The phase select signal PS_(<4:0>)initially has a binary valueequivalent to 31. This means that the rising edge of the data outputsignal should be delayed 31 unit steps from the data input signal, plusa clock cycle. The selection logic 150 unpacks the phase select signalPS_(<4:0>) and generates the selection signal S_(1<3:0>). The phaseselect signal PS_(<4:0>) with a binary value equivalent to the decimalvalue 31 results in a selection signal S_(1<3:0>) with a binary valueequivalent to the decimal value 15. The selection signal S_(1<3:0>)assumes the value 15 upon the rising edge of the phase signal P₂₄. Atthe falling edge of the data input signal, the phase select signalPS_(<4:0>) takes on the binary value equivalent to 0. After S_(1<3:0>)takes on the value 15, the selection signal S_(2<3:0>) is generated bysampling S_(1<3:0>) at the rising edge of the phase signal P₈.Accordingly, S_(2<3:0>) takes on the binary value equivalent to 15 atthe rising edge of P₈.

The data delay signal D₃₁ goes high 31 unit steps plus one clock cycleafter the data input signal DATA IN initially goes high. The selectionsignal S2 _(<3:0>) with a value of 15 causes the second high delaymultiplexer stage 108 b to select the data delay signal D₃₁ as output.The rising edge of D₃₁ causes M_(U) to transition from low to high aftera delay of t1, where t1 the relatively high internal delay of the secondhigh delay multiplexer stage 108 b.

S_(1<3:0>) transitions from 15 to 0 because the S_(1<3:0>) selectionlogic (the flip flops 152) sample PS_(<3:0>) at the next rising edge ofP₂₄. With S_(1<3:0>) at the value 0, the first high delay multiplexerstage 108 a selects the data delay signal D₀ to be supplied at theoutput. The value of D₀ is high at this transition point, so the valueof M_(L) is initially shown as high. The falling edge of D₀ causes M_(L)to transition from high to low after a delay of t1, where t1 is therelatively high internal delay of the first high delay stage 108 a. Thefirst and second high delay multiplexer stages 108 a and 108 b haveidentical internal delays of t1.

The selection signal S_(3′) controls the low delay multiplexer stage 108c. The selection signal S_(3′) is based on the selection signal S3. Theselection signal S3 is generated by sampling PS_(<4:0>) at the risingedge of P₃₁. This causes S3 to go high at the first rising edge of P₃₁.S3′ is equivalent to S3 plus the entire delay of the multiplexer 102.The delay of the multiplexer 102 is equivalent to t1+t2. Accordingly,S3′ goes high at the rising edge of P31 after a delay of t1+t2. Onepurpose of this delay is to ensure that the falling edge of S3′ willoccur between the rising edge of M_(U) and the falling edge of M_(L).The falling edge of S3′ occurs between the rising edge of M_(U) and thefalling edge of M_(L).

While S3′, the low delay multiplexer stage selects the output M_(U) ofthe low delay multiplexer stage 108 b. The rising edge of M_(U) causesDATA OUT to go high after a delay of t2, where t2 is the internal delayof the low delay multiplexer stage 108 c. Shortly after the rising edgeof M_(U), S3′ goes low, causing the low delay multiplexer stage 108 c toselect the output M_(L) of the high delay multiplexer stage 108 a. M_(L)is initially high so DATA OUT remains high until the falling edge ofM_(L). The falling edge of M_(L) causes DATA OUT to go low after thedelay of t2. The width of the output data pulse is a single unit step.This is possible, in part, because t2 is smaller than a single unitstep.

As can be seen in FIG. 2D, the delay t₁ of the high delay multiplexerstages 108 a and 108 b is much larger than a single unit step. However,the delay t₂ of the low delay multiplexer stage 110 of the multiplexer106 is much smaller than a single unit step. Because the high delaymultiplexer stages 108 a and 108 b have the same delay t₁ and the lowdelay final multiplexer stage has a delay t₂ smaller than a single unitstep, the multiplexer 106 is able to output a data pulse with the widthof a single unit step.

The multiplexer 102 is capable of outputting data output pulses withwidths corresponding to any number of unit steps between 1 and 32. Thevalues of the phase select signal PS_(<4:0>) determine the width of theoutput data pulse. Many other signal schemes can be utilized inaccording with principles of the present disclosure without departingfrom the scope of the present disclosure.

FIG. 3 is a flow diagram of a method 300 for operating a pulse widthmodulator, according to one embodiment. At 302, the method 300 includesreceiving a clock signal with a phase locked loop. At 304, the method300 includes generating, with the phase locked loop, N phase signalseach having different phases from each other and a same period T as theclock signal. At 306, the method 300 includes receiving, with a datadelay generator, a data input signal and the phase signals. At 308, themethod 300 includes generating, with the data delay generator, N datadelay signals each corresponding to the data input signal and delayed inaccordance with a respective one of the phase signals. At 310, themethod 300 includes receiving a first half of the data delay signalswith a first multiplexer stage. At 312, the method 300 includesreceiving a second half of the data delay signals with a secondmultiplexer stage having a same internal delay as the first multiplexerstage. At 314, the method 300 includes generating, with a thirdmultiplexer stage, a data output pulse having a width based on an outputof the first multiplexer stage and an output of the second multiplexerstage.

In one embodiment, a pulse width modulator includes a phase locked loopconfigured to receive a clock signal and to output N phase signals and adata delay generator configured to receive the phase signals and a datainput signal and to output N data delay signals each corresponding tothe data input signal and delayed in accordance with a respective one ofthe phase signals. The pulse width modulator includes a multiplexerhaving a first multiplexer stage configured to receive a first half ofthe data delay signals and to output a first midpoint signal, a secondmultiplexer stage in parallel with the first multiplexer stage andconfigured to receive a second half of the data delay signals and tooutput a second midpoint signal, and a third multiplexer stageconfigured to receive the first midpoint signal and the second midpointsignal and to output a data output pulse based on the first and secondmidpoint signals.

In one embodiment, a method includes receiving a clock signal with aphase locked loop, generating, with the phase locked loop, N phasesignals each having different phases from each other and a same period Tas the clock signal, and receiving, with a data delay generator, a datainput signal and the phase signals. The method includes generating, withthe data delay generator, N data delay signals each corresponding to thedata input signal and delayed in accordance with a respective one of thephase signals and receiving a first half of the data delay signals witha first multiplexer stage. The method includes receiving a second halfof the data delay signals with a second multiplexer stage having a sameinternal delay as the first multiplexer stage and generating, with athird multiplexer stage, a data output pulse having a width based on anoutput of the first multiplexer stage and an output of the secondmultiplexer stage.

In one embodiment, a pulse width modulator includes a phase locked loopconfigured to receive a clock signal having a period T and to generate Nphase signals each having the period T of the clock signal and eachoffset in time from the clock signal by a respective integer number ofunit steps. A unit step is a period of time equal to T/N. The pulsewidth modulator includes a data delay generator configured to receive adata input signal and to generate, for each phase signal, a respectivedata delay signal corresponding to the data input signal delayed inaccordance with the phase signal. The pulse width modulator includes afirst multiplexer stage configured to receive, as inputs, a first groupof N/2 of the data delay signals, a second multiplexer stage configuredto receive, as inputs, a second group of N/2 of the data delay signalsdistinct from the first group, and a third multiplexer stage configuredto receive, as inputs, an output of the first multiplexer and an outputof the second multiplexer, and to provide a data pulse having a widthbased on the output of the first multiplexer stage and the output of thesecond multiplexer stage.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

The invention claimed is:
 1. A pulse width modulator, comprising: aphase locked loop configured to receive a clock signal and to output Nphase signals; a data delay generator configured to receive the phasesignals and a data input signal and to output N data delay signals eachcorresponding to the data input signal and delayed in accordance with arespective one of the phase signals; and a multiplexer configured toreceive the N data delay signals, a first selection signal, and a secondselection signal and to output a data pulse based on the first andsecond selection signals.
 2. The pulse width modulator of claim 1,wherein the multiplexer includes: a first multiplexer stage configuredto receive a first half of the data delay signals and to output a firstmidpoint signal based on the first selection signal; a secondmultiplexer stage configured to receive a second half of the data delaysignals and to output a second midpoint signal based on the secondselection signal.
 3. The pulse width modulator of claim 2, wherein themultiplexer includes a third multiplexer stage configured to receive thefirst midpoint signal and the second midpoint signal and to output adata output pulse based on the first and second midpoint signals and thethird selection signal.
 4. The pulse width modulator of claim 3, whereinthe clock signal has a period T, wherein the third multiplexer stage isconfigured to output the data output pulse with a width equal to T/N. 5.The pulse width modulator of claim 4, wherein the first and secondmultiplexer stages have identical internal delays.
 6. The pulse widthmodulator of claim 5, wherein the third multiplexer stage has aninternal delay less than the internal delay of the first and secondmultiplexer stages.
 7. The pulse width modulator of claim 5, wherein thethird multiplexer stage has an internal delay less than T/N.
 8. Thepulse width modulator of claim 7, wherein the first multiplexer stagereceives the first selection signal locked to one of the phase signalshaving a delay equal to N*3/4 unit steps.
 9. The pulse width modulatorof claim 8, wherein the second multiplexer stage receives the secondselection signal locked to one of the phase signals having a delay equalto N/4 unit steps.
 10. The pulse width modulator of claim 9, wherein thethird multiplexer stage receives the third selection signal lock to oneof the phase signals having a delay equal to N−1 unit steps.
 11. Amethod, comprising: receiving a clock signal with a phase locked loop;generating, with the phase locked loop, N phase signals each havingdifferent phases from each other and a same period T as the clocksignal; receiving, with a data delay generator, a data input signal andthe phase signals; generating, with the data delay generator, N datadelay signals each corresponding to the data input signal and delayed inaccordance with a respective one of the phase signals; receiving, with amultiplexer, the N data delay signals; receiving, with the multiplexer,a first selection signal, a second selection signal, and a thirdselection signal; and outputting, from the multiplexer, a data outputpulse having a width based on the first, second, and third selectionsignals.
 12. The method of claim 11, comprising: receiving a first halfof the data delay signals and the first selection signal with a firstmultiplexer stage of the multiplexer; receiving a second half of thedata delay signals and the second selection signal with a secondmultiplexer stage of the multiplexer, the second multiplexer stagehaving a same internal delay as the first multiplexer stage; receivingthe third selection signal with a third multiplexer stage of themultiplexer; and generating, with the third multiplexer stage, a dataoutput pulse having a width based on an output of the first multiplexerstage and an output of the second multiplexer stage and the thirdselection signal.
 13. The method of claim 12, further comprisinggenerating the data output pulse with a rising edge based on a rising orfalling edge of the output of the first multiplexer stage or on a risingor falling edge of the output of the second multiplexer stage.
 14. Themethod of claim 12, further comprising generating the data output pulsewith a falling edge based on a rising or falling edge of the output ofthe first multiplexer stage or on a rising or falling edge of the outputof the second multiplexer stage.
 15. The method of claim 12, wherein arising edge of the data output pulse is delayed from an edge of theoutput of one of the first multiplexer stage or the second multiplexerstage by an internal delay of the third multiplexer stage, wherein afalling edge of the data output pulse is delayed from an edge of theoutput of the other of the first multiplexer stage or the secondmultiplexer stage by the internal delay of the third multiplexer stage.16. The method of claim 15, wherein the internal delay of the thirdmultiplexer stage is less than T/N, where T is a period of the clocksignal.
 17. The method of claim 12, further comprising: controlling thefirst multiplexer stage with a first selection signal latched to one ofthe phase signals received by the second multiplexer; and controllingthe second multiplexer stage with a second selected signal latched toone of the phase signals received by the first multiplexer, wherein thefirst and second selection signals are 180 degrees out of phase witheach other.
 18. A pulse width modulator, comprising: a phase locked loopconfigured to receive a clock signal having a period T and to generate Nphase signals each having the period T of the clock signal and eachoffset in time from the clock signal by a respective integer number ofunit steps, wherein a unit step is a period of time equal to T/N; a datadelay generator configured to receive a data input signal and togenerate, for each phase signal, a respective data delay signalcorresponding to the data input signal delayed in accordance with thephase signal; a multiplexer configured to receive the data delay signalsand a plurality of selection signals, wherein the multiplexer isconfigured output a data pulse having a rising edge triggered by a firstselected data delay signal and a falling edge triggered by a second datadelay signal based on the plurality of selection signals.
 19. The pulsewidth modulator of claim 18, wherein the multiplexer includes: a firstmultiplexer stage configured to receive a first group of N/2 of the datadelay signals and a first selection signal of the plurality of selectionsignals; a second multiplexer stage configured to receive a secondselection signal of the plurality of selection signals a second group ofN/2 of the data delay signals distinct from the first group; and a thirdmultiplexer stage configured to receive, as inputs, an output of thefirst multiplexer and an output of the second multiplexer, and toprovide the data pulse.
 20. The pulse width modulator of claim 19,wherein the output of the first multiplexer stage is the first selecteddata delay signal, wherein the output of the second multiplexer is thesecond selected data delay signal.